The paper — which NSA leaker Edward Snowden deliberately avoided over his fear that it would cooperate with the United States government — is now working with the Guardian on a series of stories based on documents that detail National Security Agency cooperation with its British counterpart, the Government Communications Headquarters, known as GCHQ.

“In a climate of intense pressure from the UK government, The Guardian decided to bring in a US partner to work on the GCHQ documents provided by Edward Snowden,” Guardian spokeswoman Jennifer Lindenauer said in an email. “We are continuing to work in partnership with the NYT and others to report these stories.”

The London-based newspaper has been under intense British government pressure this summer, its editor, Alan Rusbridger, revealed earlier this week.

He quoted a top government official as telling him last month: “You’ve had your debate. There’s no need to write any more.” Officials then demanded that the paper physically destroy files of which it in fact had other copies in other countries — a surreal demand Rusbridger described as “one of the more bizarre moments in the Guardian’s long history.”

The decision to publish the revelations concerning the British intelligence service jointly with the Times may give the Guardian leverage in its battle with the British government, which is trying to prevent the stories’ publication. It may also relate to the stronger protections for free speech and press freedom under the First Amendment to the U.S. Constitution; Britain has no such protections, and its Official Secrets Act is aimed at keeping government secrets secret. Sources at both papers declined to discuss the motives beyond the spokeswoman’s reference to the “climate” of pressure.

The Guardian’s Rusbridger has used the Times’s megaphone before, to spectacular effect: When the British paper’s coverage of the phone hacking scandal at News Corp. appeared to hit a dead end, a collaboration with the the Times revived it, and helped lead to criminal charges against top News Corp. executives.

The Times’s Charlie Savage and other reporters have chased the NSA story aggressively, despite Snowden’s choice to go to fillmmaker Laura Poitras, theGuardian’s Glenn Greenwald, and Barton Gellman, who has written about the documents for the Washington Post. Snowden said he did not go to the Timesbecause the paper bowed to Bush Administration demands to delay a story on warrantless wiretapping in the interest of national security; he was afraid, he said, the paper would do the same with his revelations.

Now, Times reporter Scott Shane is at work on a series of stories expected to be published next month jointly with the Guardian, a source familiar with the plans said. The source said the internal arrangement has also been the cause of some tension in the newsroom, as other national security reporters working on the NSA story — Savage and James Risen, among others — are not centrally involved in stories based on the Guardian’s documents.

The Times’s involvement in the story also brings into sharp relief a second question: Whether carrying classified documents across national borders can be an act of journalism. CNN legal analyst Jeffrey Toobin recently compared David Miranda, Greenwald’s partner, to a “drug mule” for having sought to bring a thumb drive with classified documents from Brazil into the United Kingdom; British officials detained Miranda and confiscated data he was carrying.

Now the Times or an agent for the paper, too, appears to have carried digital files from the United Kingdom across international lines into the United States. Discussions of how to partner on the documents were carried out in person between top Guardian editors and Times executive editor Jill Abramson, all of whom declined to comment on the movement of documents. But it appears likely that someone at one of the two papers physically carried a drive with Snowden’s GCHQ leaks from London to New York or Washington — exactly what Miranda was stopped at Heathrow for doing.

Abramson declined, in a brief telephone interview from Boston, to “comment on any of that,” and stressed that she would not discuss the subject on her mobile telephone because “my cell phone is not a secure line.”